1. Technical Field
The present invention relates to a vehicular headlamp including a basic lamp piece unit capable of forming a light intensity distribution pattern for a low beam and an additional lamp piece unit capable of being lighted temporarily when lighting the basic lamp piece unit.
2. Background of the Related Art
Generally, a vehicular headlamp forms a light intensity distribution pattern for a low beam having a cutoff line at an upper end edge thereof and is constituted to ensure front optical recognizability of a driver of one's own vehicle, such that glare is not cast to a driver of a vehicle running on an opposite lane or the like.
In this case, as described in, for example, JP-A-2000-238576 or JP-A-2001-213227, a related art vehicular headlamp includes an additional lamp piece unit that irradiates light for forming an additional light intensity distribution pattern by being lighted temporarily in lighting a basic lamp piece unit other than the basic lamp piece unit constituted to be able to irradiate light for forming a light intensity distribution pattern for a low beam.
By including the additional lamp piece unit other than the basic lamp piece unit, sufficient front optical recognizability can be ensured even under a running situation in which the sufficient front optical recognizability is difficult to achieve by a normal light intensity distribution pattern for a low beam. For example, when the additional lamp piece unit is provided to form the additional light intensity distribution pattern in a side direction of the light intensity distribution pattern for a low beam and the additional lamp piece unit is additionally lighted in running the vehicle to turn, a front road face in a turning direction can sufficiently be irradiated.
However, according to the vehicular headlamp described in the above-cited related art, a light source bulb of a discharge bulb, a halogen bulb or the like is used not only for the basic lamp piece unit but also for the additional lamp piece unit as light sources thereof. Therefore, at least the following problem is posed.
Although the additional lamp piece unit is lighted on and off repeatedly in accordance with the situation of running the vehicle, there is a related art problem in that a response speed of the light source bulb in lighting on and off the light source bulb is not so fast. Therefore, there is a related art problem in that the light source bulb is not sufficient in irradiating light in correspondence with the situation of running the vehicle.
Further, there is a related art problem in that by frequently repeating to light on and off the light source bulb, life of the light source bulb is shortened.
Additionally, when the light source bulb is used in the related art, there also is a problem in that a size of the additional lamp piece unit is enlarged to some degree. Therefore, it is not easy to arrange the additional lamp piece unit to form the aimed additional light intensity distribution pattern.